Pharmacokinetics, clinical efficacy and safety of acetaminophen (paracetamol) in adult horses with naturally occurring chronic lameness.

Abstract

BACKGROUND:

Acetaminophen is used clinically in horses with musculoskeletal pain; however, no studies have been performed in horses with chronic lameness.

OBJECTIVES:

To determine the pharmacokinetics, safety and efficacy of chronic dosing of acetaminophen in horses with naturally occurring chronic lameness.

STUDY DESIGN:

Longitudinal.

METHODS:

Twelve adult horses with chronic lameness were treated with acetaminophen (30 mg/kg PO) every 12 h for 21 days. Plasma concentrations of acetaminophen were analysed on days 7 and 21 via LC-MS/MS and noncompartmental pharmacokinetic analysis. Lameness was evaluated by body-mounted inertial sensor (BMIS) and 10-point subjective lameness score on day 21 and compared to untreated baseline evaluation on day 35. Clinicopathological analysis (n = 12), hepatic biopsy (n = 6) and gastroscopy (n = 6) were evaluated on days -1 and 22.

RESULTS:

Maximum plasma acetaminophen concentration (Cmax ) was 20.83 ± 10.25 μg/mL at time (Tmax ) 0.40 ± 0.22 h on day 7. The Cmax on day 21 was 17.33 ± 6.91 μg/mL with a Tmax of 0.67 ± 0.26 h. Subjective lameness scores significantly improved at 2 and 4 h post-treatment; Significant percent improvement was detected in PDmax for horses with hindlimb lameness at 1, 2 and 8 h post-treatment. There were no significant differences in gastroscopy or hepatic biopsy scores between days -1 and 22.

MAIN LIMITATIONS:

Small sample size, multi-limb lameness of varying severity and aetiology, lack of intermediary lameness evaluation.

CONCLUSIONS:

In horses with naturally occurring chronic lameness, acetaminophen at 30 mg/kg produced a transient improvement in subjective lameness and BMIS evaluation. Acetaminophen may not be effective as a monotherapy. Acetaminophen was safe following 21 days of 30 mg/kg PO every 12 h, with no evidence of clinically significant changes in clinicopathological analysis, hepatic biopsy or gastric ulceration scores.

• Authors: Melissa A Mercer, Jennifer L Davis, Harold C McKenzie, Christopher R Byron, Maureen E Kelleher, Lauren Trager, Thomas E Cecere, Katie E Wilson, R M Council-Troche, Stephen R Werre
• Journal: Equine veterinary journal (Equine Vet J) (Jun 07 2023) ISSN: 2042-3306 [Electronic] United States
• PMID: 37287331 (Publication Type: Journal Article)
• Copyright: © 2023 EVJ Ltd.